Multiple in-vehicle apparatuses are attached to a vehicle, and two of the multiple in-vehicle apparatuses may communicate with one another by transmitting a signal through a transmission line. The communication signal includes a harmonic, so a harmonic noise radiates from the transmission line.
In order to suppress the harmonic noise, various types of radiation noise reduction techniques have been developed (see, e.g., Patent Literature 1). The invention disclosed in Patent Literature 1 limits a frequency band of a rectangular signal so as to reduce the radiation noise.